1. Field of the Invention
The present invention relates to semiconductor physical quantity sensing devices such as pressure sensors, acceleration sensors, and the like used in various kinds of apparatuses for automotive use, medical use, industrial use, etc., and more particularly to semiconductor physical quantity sensing devices having a configuration which performs sensitivity adjustment, adjustment of temperature characteristics, offset adjustment, etc., by way of electric trimming using an EPROM.
2. Description of the Related Art
Recently, electric trimming methods and apparatuses for adjusting the output characteristics of physical quantity sensors enable adjustment after an assembly process, because conventional laser trimming methods have the disadvantage of not permitting re-adjustment even when a variation in output characteristics occurs during the assembly process following trimming. However, electric trimming results in increased manufacturing costs caused by an increase in the number of wire bonding points, due to the need for numerous control terminals for inputting/outputting trimming data, writing data into the EPROM, etc. In order to solve this problem, proposals have been made to perform electric trimming with a small number of terminals by creating a plurality of terminal operation threshold voltages by using resistive potential division and bipolar transistors. (For example Japanese Patent Application Laid-open No. Hei6-29555.)
However, since the above-mentioned proposal uses bipolar transistors, with a mixing of EPROM(s) made by the CMOS process with bipolar transistors, the BiCMOS process becomes necessary, which has the disadvantage of inviting cost increases. To solve this problem, the use of MOS transistors, in place of the bipolar transistors in the above-mentioned proposal, has been considered. However, in such a case, the upper limit of the threshold voltages that can be set with MOS transistors is lower than with bipolar transistors, so the spacing between the plurality of thresholds becomes smaller and there is the disadvantage that mis-operation is more likely to occur. To prevent such problems, it is necessary to increase the upper limit of the threshold voltages to a level equal to that of bipolar transistors but to do that, it is necessary to make MOS transistors capable of higher voltage tolerances and to add new protection circuits, which has the problem of inviting further cost increases.